Brits go to the polls today in a crucial set of local and mayoral elections

The leader of Britain's opposition Labour Party, Jeremy Corbyn, leaves his home in London, Britain April 19, 2017. REUTERS/Hannah McKay Reuters / Hannah McKay LONDON — Large parts of Britain go to the polls today in the last major electoral test before the upcoming general election.

Voting got underway at 7:00 (BST) this morning, with a total of 4,851 council seats across England, Wales and Scotland up for grabs. A series of important mayoral elections are also taking place in six English regions.

These local and mayoral elections are unusual because they come just five weeks before voters will go back to the polls for the general election, and slap-bang in the middle of the political parties' election campaigns.

With this in mind, the results of today's elections, expected on Friday, could provide big clues as to how the parties will perform at the general election on June 8.

The Tories are currently crushing Labour in the polls and look set to enjoy a successful day at the expense of the struggling opposition party.

Theresa May's party is expected to make over 100 net gains at council level and could inflict a huge blow to Jeremy Corbyn's Labour if Conservative candidate Andy Street defeats Labour's Siôn Simon to win the West Midlands mayoral election. Labour had a 9.4% lead over the Tories at the 2015 general election, the Centre for Cities estimates.

It'll also be interesting to see how UKIP and the Liberal Democrats perform.

One in four voters backed UKIP in the 2013 local elections but polls suggest the Paul Nuttall-party is steadily in decline and could suffer around 105 net losses today. The Lib Dems, on the other hand, could make up 90 net gains.

Tim Farron's party has reaped the rewards since becoming the country's leading anti-Brexit party, including a stunning victory in December's by-election in Richmond Park, where the Tory to Lib Dem swing was a huge 21.73%.

Counting in some councils will get underway tonight shortly after the polls close at 22:00 (BST) with others set to begin counting on Friday morning. Results will be announced throughout the day on Friday.